Preparation method of hydrophobic double-layer polymer asymmetric composite membrane

Abstract

The invention discloses a method for preparing a hydrophobic double-layer polymer asymmetric composite membrane, which comprises the following steps: (1) preparing a porous support layer base membrane; (2) preparing a colloidal emulsion: dissolving PDMS in n-heptane, adding distilled water, sodium dodecylbenzenesulfonate and hexadecyltrimethoxysilane to the solution obtained by stirring, stirring evenly, and then performing high-speed shear stirring, and then vacuuming and performing high-speed shear stirring again to obtain a white colloidal emulsion; (3) preparing a dense separation layer membrane liquid: adding nano-SiO 2 , NaOH, and diethanolamine, stir evenly, then add vinyl triethylsilane and zinc ethylenediaminetetraacetate, stir and then perform high-speed shear stirring to obtain a dense separation layer membrane liquid; (4) discharge treat the surface of the porous support layer base membrane; (5) coat the dense separation layer membrane liquid on the base membrane after the discharge treatment, dry and cool it down, then take it out to obtain a hydrophobic double-layer polymer asymmetric composite membrane.

Description

Technical Field

[0001] The invention relates to a method for preparing a hydrophobic double-layer polymer asymmetric composite membrane, belonging to the technical field of polymer composite membranes. Background Art

[0002] The polymer composite membrane with a hydrophobic double-layer asymmetric structure can exhibit a variety of gas separation and purification functions, such as pervaporation, molecular sieving, Knudsen diffusion, etc. Therefore, it is widely used in the concentration, purification, and purification of gases such as condensable gas and non-condensable gas separation, polar gas and non-polar gas separation.

[0003] The typical structural feature of the hydrophobic double-layer asymmetric polymer composite membrane is that a dense hydrophobic surface film structure is covered on the porous support layer base membrane of the polymer material. This hydrophobic surface film structure, as a separation layer membrane, is the key to determining the membrane separation performance. The commonly used preparation methods include surface grafting, surface polymerization, blending and other methods. In practical applications, these methods often have the disadvantages of high unevenness of the combination of the separation layer membrane and the base membrane and poor repeatability, resulting in large dispersion of the separation performance of the prepared double-layer membrane at different positions, resulting in a decrease in the overall separation performance of the double-layer membrane. This phenomenon is particularly prominent in asymmetric composite membranes with a dense layer of cross-linked polydimethylsiloxane (PDMS) as the separation layer and polyvinylidene fluoride (PVDF), polyetherimide (PEI) or polyacrylonitrile (PAN) as the porous support layer base membrane. The separation coefficient and gas flux of the membrane prepared by the existing technology can differ by as much as 2 to 5 times at different positions per square meter, which greatly interferes with practical applications. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a hydrophobic double-layer polymer asymmetric composite membrane, so as to solve the technical problem that the separation performance of the double-layer membrane at different positions in the prior art varies greatly.

[0005] The present invention adopts the following technical scheme: A method for preparing a hydrophobic double-layer polymer asymmetric composite membrane, comprising the following steps: (1) preparing a porous support layer base membrane: dissolving PVDF or PEI or PAN or PSA or PSF or PES as a base membrane raw material in a solvent, wherein the solvent is DMAC or NMP or DMF or DMSO, and adding 1 to 5 wt.% of hydrophilic nano-SiO2 powder and 1 to 5 wt.% of diethylamine at the same time, dissolving and stirring evenly, vacuuming and degassing to obtain a base membrane solution, and then coating the base membrane solution on a non-woven fabric, and coating the base membrane solution on a non-woven fabric. The non-woven fabric is immersed in pure water until the solvent is completely exchanged into the water, and then taken out and dried in the shade to obtain a porous support layer base film; (2) preparing a colloidal emulsion: dissolving PDMS in n-heptane, stirring to fully dissolve PDMS, and obtaining a solution with a PDMS mass ratio of 10% to 20%, taking 100 parts by weight of the solution, adding 100 to 300 parts by weight of distilled water, 10 to 30 parts by weight of sodium dodecylbenzene sulfonate, and 5 to 20 parts by weight of hexadecyltrimethoxysilane, stirring evenly, and then performing high-speed shear stirring to form a solution containing micro- The emulsion is then vacuumed for a period of time to remove the n-heptane solvent in the emulsion, and then high-speed shear stirring is continued to obtain a white colloidal emulsion without n-heptane; (3) dense separation layer membrane liquid: 100 parts by weight of the colloidal emulsion prepared in step (2) is taken, and then 5 to 20 parts by weight of nano-SiO2, 1 to 5 parts by weight of NaOH, and 3 to 8 parts by weight of diethanolamine are added, and stirred evenly, and then 5 to 10 parts by weight of vinyl triethyl silane and 1 to 5 parts by weight of zinc ethylenediaminetetraacetate are added, and stirred evenly. The mixture is mixed evenly and then subjected to high-speed shear stirring to obtain a dense separation layer membrane liquid; (4) base membrane discharge treatment: the porous support layer base membrane prepared in step (1) is placed in a space with a relative humidity of 70-80% RH and a temperature of 20-50°C for 2-4 hours, and then the base membrane surface is subjected to discharge treatment; (5) coating a dense separation layer membrane liquid: the dense separation layer membrane liquid obtained in step (3) is coated on the base membrane after the discharge treatment in step (4), the base membrane after discharge being a flat base membrane or a hollow fiber base membrane, dried for a period of time, and taken out after cooling to obtain a hydrophobic double-layer polymer asymmetric composite membrane.

[0006] In step (1), the base film solution is coated on the non-woven fabric using a scraper.

[0007] In step (1), the non-woven fabric coated with the base film solution is immersed in pure water for two to three days.

[0008] In step (2), PDMS with a molecular weight of 50,000 to 300,000 is used, and the PDMS is dissolved in n-heptane with a stirring time of 4 hours.

[0009] In step (2), after adding distilled water, sodium dodecylbenzenesulfonate and hexadecyltrimethoxysilane to the n-heptane solution containing PDMS, the stirring time is 2-4 hours; the speed of the two high-speed shear stirrings is 5000-10000 r / min, and the time is 10-30 minutes.

[0010] In step (2), the vacuuming temperature is 30°C to 60°C, the vacuuming time is 4 to 8 hours, and the vacuuming pressure is -10 kPa to -60 kPa.

[0011] In step (3), the stirring time is 2 h, the speed of high-speed shear stirring is 5000-10000 r / min, and the time is 10-30 min.

[0012] In step (4), the specific step of the discharge treatment is to use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined, and brush back and forth 2 to 3 times.

[0013] In step (5), the dense separation layer membrane liquid is coated by blade coating or casting, and the coating amount of the dense separation layer is 20-50g / m 2 .

[0014] In step (5), the drying is carried out in two stages, firstly at 60°C for 2 to 4 hours, and then at no more than 120°C for another 4 to 12 hours.

[0015] The beneficial effects of the present invention are as follows: the hydrophilicity of the surface of the base membrane can be improved by adding hydrophilic nano-SiO2 powder into the base membrane, and diethylamine makes the SiO2 powder evenly distributed in the base membrane solution; the silica sol formed by nano-SiO2 and NaOH is used as a cross-linking agent, and vinyl triethyl silane is used as another cross-linking agent, and PDMS and the cross-linking agent form an aqueous colloidal emulsion; by adding SiO2 into the base membrane support layer and subjecting the base membrane support layer to a low-temperature plasma discharge treatment, a large number of hydrophilic groups are provided on the surface of the base membrane, thereby improving the hydrophilicity of the surface of the base membrane, and when a separation layer membrane liquid whose main component is water is coated on the surface, the separation layer membrane liquid has a strong wettability with the base membrane, and the separation layer membrane liquid will not agglomerate and then disperse on the base membrane due to the hydrophobicity of the base membrane, thereby ensuring the even distribution of the coating liquid.

[0016] In general, the present invention forms an aqueous colloidal emulsion with PDMS and a cross-linking agent, and by improving the hydrophilicity of the support layer, the uniformity of the distribution of the separation layer preparation material on the surface of the support layer is greatly improved, and a separation layer membrane material with good uniformity and consistency can be obtained, thereby improving the uniformity of the membrane separation performance and the overall working effect.

[0017] The hydrophobic double-layer polymer asymmetric composite membrane prepared by the present invention has good uniformity of dense separation layer, and the difference of separation coefficient in different areas per square meter is less than 35%. Moreover, by adjusting the coating amount of dense separation layer membrane liquid, high permeation flux for N2, O2, dichloromethane and n-hexane can be obtained, and the permeation flux of N2 reaches 120-180 GPU, the permeation flux of O2 reaches 250-400 GPU, the permeation flux of dichloromethane can reach 4800-6200 GPU, and the permeation flux of n-hexane can reach 5300-7800 GPU. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is an electron microscope image of a cross section of a membrane prepared in Example 1 of the present invention;

[0019] Figure 2 is an electron microscope image of the membrane surface prepared in Example 1 of the present invention;

[0020] Figure 3 These are the results of separation experiments and permeation experiments on the hydrophobic double-layer polymer asymmetric composite membranes prepared in Examples 1-4. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] The method for preparing the hydrophobic double-layer polymer asymmetric composite membrane of the present invention comprises the following steps:

[0023] (1) Preparation of porous supporting layer base membrane: PVDF (polyvinylidene fluoride) or PEI (polyethylene imine) or PAN (polyacrylonitrile) or PSA (polysulfone amide) or PSF (polysulfone) or PES (polyether sulfone) as base membrane raw materials are dissolved in a solvent, wherein the solvent is DMAC (N, N-dimethylacetamide) or NMP (N-methylpyrrolidone) or DMF (N, N-dimethylformamide) or DMSO (dimethyl sulfoxide), and 1 to 5 wt.% of hydrophilic nano-SiO2 powder and 1 to 5 wt.% of diethylamine are added at the same time. After dissolving and stirring evenly, vacuum degassing treatment is performed to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric with a scraper. Subsequently, the non-woven fabric coated with the base membrane solution is immersed in pure water for two to three days until the solvent is completely exchanged into water, and then taken out and dried in the shade to obtain a porous supporting layer base membrane.

[0024] In this step, the hydrophilic nano-SiO2 powder can increase the hydrophilicity of the base membrane surface so that the separation layer membrane liquid can be more evenly distributed on the base membrane surface; diethylamine plays a role in evenly distributing the hydrophilic nano-SiO2 powder and avoiding agglomeration; pure water immersion is to exchange the solvent into water, thereby solidifying the dissolved base membrane raw material polymer material to form a layer of base membrane combined with the non-woven fabric.

[0025] (2) Preparation of colloidal emulsion: Dissolve PDMS (polydimethylsiloxane) with a molecular weight of 50,000 to 300,000 in n-heptane at a mass ratio of 10% to 20%, stir for 4 hours to fully dissolve the PDMS, take 100 g of the solution, add 100 g to 300 g of distilled water, 10 to 30 g of sodium dodecylbenzene sulfonate, and 5 g to 20 g of hexadecyltrimethoxysilane to the solution, stir for 2 to 4 hours, and then perform high-speed shear stirring at a speed of 5000 to 10000 r / min for 10 to 30 minutes to form an emulsion containing micro-colloids, and then evacuate (-10 kPa to -60 kPa) at 30°C to 60°C for 4 to 8 hours to remove the n-heptane solvent in the emulsion, and then continue to perform high-speed shear stirring at a speed of 5000 to 10000 r / min for 10 to 30 minutes to obtain a large white colloidal emulsion without n-heptane.

[0026] The sodium dodecylbenzenesulfonate and hexadecyltrimethoxysilane components added in this step are both used as surfactants to make the solution become an emulsion containing micro-particle colloids through high-speed shear stirring.

[0027] (3) Preparation of dense separation layer membrane liquid: Take 100 g of the colloidal emulsion prepared in step (2), then add 5 g to 20 g of nano-SiO2, 1 g to 5 g of NaOH, and 3 g to 8 g of diethanolamine, stir for 2 h, then add 5 g to 10 g of vinyl triethylsilane and 1 g to 5 g of zinc ethylenediaminetetraacetate, stir for 4 h, and perform high-speed shear stirring at a speed of 5000 to 10000 r / min for 10 to 30 min to obtain a dense separation layer membrane liquid.

[0028] In this step, the added nano-SiO2 is used to form a silicon-containing sol as a cross-linking agent with NaOH, and diethanolamine is used to adjust the viscosity and dispersion of the silica sol. After the reaction is evenly mixed, vinyl triethyl silane is added as the second silicon-containing cross-linking agent, and zinc ethylenediaminetetraacetate is a catalyst that promotes the cross-linking of the silicon cross-linking agent with PDMS. Then, a micro-particle colloidal emulsion with uniformly mixed components is obtained through high-speed shear stirring.

[0029] (4) Discharge treatment of base film: Take the porous support layer base film prepared in step (1), place it in a space with a relative humidity of 70-80%RH and a temperature of 20-50°C for 2-4 hours, and then use a comb-shaped low-temperature plasma brush to discharge the surface of the base film and the dense separation layer membrane liquid and brush it back and forth 2-3 times. The purpose of discharge is to generate a large number of hydroxyl groups on the surface of the base film through the action of low-temperature plasma to improve the hydrophilicity of the base film, thereby increasing the coating uniformity of the base film and the separation layer membrane liquid.

[0030] (5) Coating the dense separation layer membrane liquid: Use a doctor blade or casting method to coat the dense separation layer membrane liquid on the porous support layer base membrane after the discharge treatment in step (4). It can be a flat base membrane or a hollow fiber base membrane. The dense separation layer coating amount is 20-50g / m 2 First, bake at 60°C for 2 to 4 hours to dry out the moisture, then continue baking at no more than 120°C for 4 to 12 hours, cross-link at this temperature, and then cool and take out to obtain the target product, a hydrophobic double-layer polymer asymmetric composite membrane.

[0031] The following specific embodiments are tested according to the above method:

[0032] Embodiment 1:

[0033] The preparation method of the hydrophobic double-layer polymer asymmetric composite membrane of this embodiment is carried out according to the following steps:

[0034] (1) Preparation of porous supporting layer base membrane: 18 g PVDF as base membrane raw material is dissolved in a solvent, the solvent is 80 g DMAC, and 1 g hydrophilic nano-SiO2 powder and 1 g diethylamine are added at the same time. After dissolution and stirring evenly, vacuum degassing treatment is performed to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric with a scraper. Subsequently, the non-woven fabric coated with the base membrane solution is immersed in pure water for three days until the solvent is completely exchanged into water. After taking out, it is dried in the shade to obtain a porous supporting layer base membrane.

[0035] (2) Preparation of colloidal emulsion: Dissolve 20 g of PDMS with a molecular weight of 50,000 in 180 g of n-heptane at a mass ratio and stir for 4 h to fully dissolve the PDMS. Take 100 g of the solution, add 100 g of distilled water, 10 g of sodium dodecylbenzenesulfonate and 5 g of hexadecyltrimethoxysilane to the solution and stir for 2 h. Then, high-speed shear stirring is performed at a speed of 5000 r / min for 30 min to form an emulsion containing micro-colloids. Then, vacuum is drawn at a temperature of 30°C and a pressure of -10 kPa for 4 h to remove the n-heptane solvent in the emulsion. Then, high-speed shear stirring is continued at a speed of 5000 r / min for 30 min to obtain a white colloidal emulsion that does not contain n-heptane.

[0036] (3) Preparation of dense separation layer membrane liquid: Take 100 g of the colloidal emulsion prepared in step (2), then add 5 g of nano-SiO2, 1 g of NaOH, and 3 g of diethanolamine, stir for 2 h, then add 5 g of vinyl triethylsilane and 1 g of zinc ethylenediaminetetraacetate, stir for 4 h, and perform high-speed shear stirring at a speed of 5000 r / min for 30 min to obtain a dense separation layer membrane liquid.

[0037] (4) Discharge treatment of base membrane: Take the porous support layer base membrane prepared in step (1) and place it in a space with a relative humidity of 70% RH and a temperature of 20°C for 2 h. Then use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined and brush it back and forth twice.

[0038] (5) Coating the dense separation layer membrane liquid: Use a doctor blade or cast method to coat the dense separation layer membrane liquid on the porous support layer base membrane after the discharge treatment in step (4). The porous support layer base membrane is a flat base membrane. The membrane liquid coating amount is 28g / m 2 First, bake at 60°C for 2 hours to dry out the moisture, then continue baking at 120°C for 4 hours, cross-link at this temperature, and then cool and take out to obtain the target product, a hydrophobic double-layer polymer asymmetric composite membrane.

[0039] Embodiment 2:

[0040] The preparation method of the hydrophobic double-layer polymer asymmetric composite membrane of this embodiment is carried out according to the following steps:

[0041] (1) Preparation of porous supporting layer base membrane: 16 g PEI as base membrane raw material is dissolved in a solvent, the solvent is 74 g NMP, and 5 g hydrophilic nano-SiO2 powder and 5 g diethylamine are added at the same time. After dissolution and stirring evenly, vacuum degassing treatment is performed to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric with a scraper. Subsequently, the non-woven fabric coated with the base membrane solution is immersed in pure water for three days until the solvent is completely exchanged into water. After taking out, it is dried in the shade to obtain a porous supporting layer base membrane.

[0042] (2) Preparation of colloidal emulsion: Dissolve PDMS with a molecular weight of 300,000 and a weight of 40 g in 160 g of n-heptane at a mass ratio, stir for 4 h to fully dissolve the PDMS, take 100 g of the solution, add 300 g of distilled water, 30 g of sodium dodecylbenzenesulfonate, and 20 g of hexadecyltrimethoxysilane to the solution, stir for 2 h, and then perform high-speed shear stirring at a speed of 10,000 r / min for 10 min to form an emulsion containing micro-colloids in the solution, and then evacuate the solution at a temperature of 60°C and a pressure of -60 kPa for 8 h to remove the n-heptane solvent in the emulsion, and then continue to perform high-speed shear stirring at a speed of 10,000 r / min for 10 min to obtain a white colloidal emulsion that does not contain n-heptane.

[0043] (3) Preparation of dense separation layer membrane liquid: Take 100 g of the colloidal emulsion prepared in step (2), then add 20 g of nano-SiO2, 5 g of NaOH, and 8 g of diethanolamine, stir for 2 h, then add 10 g of vinyl triethylsilane and 5 g of zinc ethylenediaminetetraacetate, stir for 4 h, and perform high-speed shear stirring at a speed of 10,000 r / min for 10 min to obtain a dense separation layer membrane liquid.

[0044] (4) Discharge treatment of base membrane: Take the porous support layer base membrane prepared in step (1) and place it in a space with a relative humidity of 80% RH and a temperature of 50°C for 4 hours. Then, use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined, and brush it back and forth 3 times.

[0045] (5) Coating the dense separation layer membrane liquid: Use a doctor blade or casting method to coat the dense separation layer membrane liquid on the porous support layer base membrane after the discharge treatment in step (4). The porous support layer base membrane is a hollow fiber base membrane. The membrane liquid coating amount is 25g / m 2 First, bake at 60°C for 4 hours to dry out the moisture, then continue baking at 120°C for 12 hours, cross-link at this temperature, and then cool and take out to obtain the target product, a hydrophobic double-layer polymer asymmetric composite membrane.

[0046] Embodiment 3:

[0047] The preparation method of the hydrophobic double-layer polymer asymmetric composite membrane of this embodiment is carried out according to the following steps:

[0048] (1) Preparation of porous supporting layer base membrane: 18 g PAN as the base membrane raw material is dissolved in a solvent, the solvent is 78 g DMF, and 2 g of hydrophilic nano-SiO2 powder and 3 g% diethylamine are added at the same time. After dissolution and stirring evenly, vacuum degassing treatment is performed to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric with a scraper. Subsequently, the non-woven fabric coated with the base membrane solution is immersed in pure water for two days until the solvent is completely exchanged into water. After taking out, it is dried in the shade to obtain a porous supporting layer base membrane.

[0049] (2) Preparation of colloidal emulsion: Take 20 g of PDMS with a molecular weight of 200,000 and a weight of 20 g and dissolve it in 170 g of n-heptane at a mass ratio, stir for 4 h to fully dissolve the PDMS, take 100 g of the solution, add 200 g of distilled water, 20 g of sodium dodecylbenzenesulfonate and 10 g of hexadecyltrimethoxysilane to the solution, stir for 3 h, and then perform high-speed shear stirring at a speed of 8000 r / min for 20 min to form an emulsion containing micro-colloids in the solution, and then evacuate the solution at a temperature of 40°C and a pressure of -30 kPa for 5 h to remove the n-heptane solvent in the emulsion, and then continue to perform high-speed shear stirring at a speed of 8000 r / min for 20 min to obtain a white colloidal emulsion without n-heptane.

[0050] (3) Preparation of dense separation layer membrane liquid: Take 100 g of the colloidal emulsion prepared in step (2), then add 10 g of nano-SiO2, 2 g of NaOH, and 5 g of diethanolamine, stir for 2 h, then add 8 g of vinyl triethylsilane and 2 g of zinc ethylenediaminetetraacetate, stir for 4 h, and perform high-speed shear stirring at a speed of 8000 r / min for 20 min to obtain a dense separation layer membrane liquid.

[0051] (4) Discharge treatment of base membrane: Take the porous support layer base membrane prepared in step (1) and place it in a space with a relative humidity of 70% RH and a temperature of 20°C for 2 h. Then use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined and brush it back and forth twice.

[0052] (5) Coating the dense separation layer membrane liquid: Use a doctor blade or casting method to coat the dense separation layer membrane liquid on the porous support layer base membrane after the discharge treatment in step (4). The porous support layer base membrane is a hollow fiber base membrane. The membrane liquid coating amount is 34g / m 2 First, bake at 60°C for 2 hours to dry out the moisture, then continue baking at 100°C for 8 hours, cross-link at this temperature, and then cool down and take out to obtain the target product, a hydrophobic double-layer polymer asymmetric composite membrane.

[0053] Embodiment 4:

[0054] The preparation method of the hydrophobic double-layer polymer asymmetric composite membrane of this embodiment is carried out according to the following steps:

[0055] (1) Preparation of porous supporting layer base membrane: 20 g PSA as base membrane raw material is dissolved in a solvent, the solvent is 80 g DMSO, and 2 g hydrophilic nano-SiO2 powder and 2 g diethylamine are added at the same time. After dissolution and stirring evenly, vacuum degassing treatment is performed to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric with a scraper. Subsequently, the non-woven fabric coated with the base membrane solution is soaked in pure water for two to three days until the solvent is completely exchanged into water. After taking out, it is dried in the shade to obtain a porous supporting layer base membrane.

[0056] (2) Preparation of colloidal emulsion: Dissolve 20 g of PDMS with a molecular weight of 100,000 in 180 g of n-heptane at a mass ratio and stir for 4 h to fully dissolve the PDMS. Take 100 g of the solution, add 150 g of distilled water, 15 g of sodium dodecylbenzenesulfonate and 15 g of hexadecyltrimethoxysilane to the solution and stir for 4 h. Then, high-speed shear stirring is performed at a speed of 10,000 r / min for 25 min to form an emulsion containing micro-colloids. Then, vacuum is drawn at a temperature of 50°C and a pressure of -40 kPa for 4 h to remove the n-heptane solvent in the emulsion. Then, high-speed shear stirring is continued at a speed of 10,000 r / min for 25 min to obtain a white colloidal emulsion that does not contain n-heptane.

[0057] (3) Preparation of dense separation layer membrane liquid: Take 100 g of the colloidal emulsion prepared in step (2), then add 15 g of nano-SiO2, 3 g of NaOH, and 6 g of diethanolamine, stir for 2 h, then add 6 g of vinyl triethylsilane and 3 g of zinc ethylenediaminetetraacetate, stir for 4 h, and perform high-speed shear stirring at a speed of 10,000 r / min for 25 min to obtain a dense separation layer membrane liquid.

[0058] (4) Discharge treatment of base membrane: Take the porous support layer base membrane prepared in step (1) and place it in a space with a relative humidity of 80% RH and a temperature of 50°C for 4 hours. Then, use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined, and brush it back and forth 3 times.

[0059] (5) Coating the dense separation layer membrane liquid: Use a doctor blade or cast method to coat the dense separation layer membrane liquid on the porous support layer base membrane after the discharge treatment in step (4). The porous support layer base membrane is a flat base membrane. The membrane liquid coating amount is 37g / m 2 First, bake at 60°C for 4 hours to dry out the moisture, then continue baking at 100°C for 12 hours, cross-link at this temperature, and then cool down and take out to obtain the target product, a hydrophobic double-layer polymer asymmetric composite membrane.

[0060] The hydrophobic double-layer polymer asymmetric composite membranes prepared in Examples 1-4 were subjected to separation experiments and permeation experiments. The experimental results are as follows: Figure 3 As shown in the table. Figure 3 It can be seen that the composite membranes of Examples 1-4 have high separation coefficients and high permeation fluxes for N2, O2, dichloromethane and n-hexane.

[0061] The permeation flux is measured using the differential pressure method, that is, pressurized gas to be measured (such as N2) is introduced into one side of the membrane, and the other side is at normal pressure. The gas flow rate that permeates the membrane is measured, and then the permeation flux is calculated based on the membrane area and the pressure difference on both sides of the membrane.

[0062] In addition, the prepared composite membrane is also subjected to a uniformity test. The uniformity test is performed by cutting small membrane pieces at different positions in a membrane (such as a membrane with an area of ​​1 square meter), measuring the permeability coefficient and separation coefficient of the membrane piece to the gas, and then comparing the multiples of the permeability coefficient and the separation coefficient of the membrane pieces at different positions. The larger the multiple, the greater the difference in non-uniformity. After testing, the hydrophobic double-layer polymer asymmetric composite membrane prepared by the present invention has good uniformity of dense separation layer, and the difference in separation coefficient of different areas per square meter is less than 35%.

[0063] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. The scope of the present invention defined by the appended claims includes all equivalent substitutions and changes.

Claims

1. A method for preparing a hydrophobic double-layer polymer asymmetric composite membrane, characterized in that: It includes the following steps: (1) Preparation of porous support layer base membrane: PVDF or PEI or PAN or PSA or PSF or PES as base membrane raw materials are dissolved in a solvent, the solvent is DMAC or NMP or DMF or DMSO, and 1-5 wt.% of hydrophilic nano-SiO2 powder and 1-5 wt.% of diethylamine are added at the same time, dissolved and stirred evenly, vacuum degassing to obtain a base membrane solution, and then the base membrane solution is coated on a non-woven fabric, and the non-woven fabric coated with the base membrane solution is immersed in pure water until the solvent is completely exchanged into water, and then taken out and dried in the shade to obtain a porous support layer. (2) preparing a colloidal emulsion: dissolving PDMS in n-heptane, stirring to fully dissolve PDMS, obtaining a solution with a PDMS mass ratio of 10% to 20%, taking 100 parts by weight of the solution, adding 100 to 300 parts by weight of distilled water, 10 to 30 parts by weight of sodium dodecylbenzenesulfonate, and 5 to 20 parts by weight of hexadecyltrimethoxysilane, stirring evenly, and then subjecting the solution to high-speed shear stirring to form an emulsion containing micro-colloids, and then vacuuming for a period of time to remove the emulsion. n-heptane solvent, and then continue to stir at a high speed to obtain a white colloidal emulsion without n-heptane; (3) dense separation layer membrane liquid: take 100 parts by weight of the colloidal emulsion prepared in step (2), then add 5 to 20 parts by weight of nano-SiO2, 1 to 5 parts by weight of NaOH, 3 to 8 parts by weight of diethanolamine, stir evenly, then add 5 to 10 parts by weight of vinyl triethyl silane, 1 to 5 parts by weight of zinc ethylenediamine tetraacetate, stir evenly, and then stir at a high speed. , obtaining a dense separation layer membrane liquid; (4) base membrane discharge treatment: placing the porous support layer base membrane prepared in step (1) in a space with a relative humidity of 70-80% RH and a temperature of 20-50°C for 2-4 hours, and then subjecting the base membrane surface to a discharge treatment; (5) coating a dense separation layer membrane liquid: coating the dense separation layer membrane liquid obtained in step (3) on the base membrane after the discharge treatment in step (4), the base membrane after discharge being a flat base membrane or a hollow fiber base membrane, drying for a period of time, and taking it out after cooling to obtain a hydrophobic double-layer polymer asymmetric composite membrane.

2. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (1), the base film solution is coated on the non-woven fabric using a scraper.

3. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (1), the non-woven fabric coated with the base film solution is immersed in pure water for two to three days.

4. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (2), PDMS with a molecular weight of 50,000 to 300,000 is used, and the PDMS is dissolved in n-heptane with a stirring time of 4 hours.

5. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (2), after adding distilled water, sodium dodecylbenzenesulfonate and hexadecyltrimethoxysilane to the n-heptane solution containing PDMS, the stirring time is 2-4 hours; the speed of the two high-speed shear stirrings is 5000-10000 r / min, and the time is 10-30 minutes.

6. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (2), the vacuuming temperature is 30°C to 60°C, the vacuuming time is 4 to 8 hours, and the vacuuming pressure is -10 kPa to -60 kPa.

7. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (3), the stirring time is 2 h, the speed of high-speed shear stirring is 5000-10000 r / min, and the time is 10-30 min.

8. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (4), the specific step of the discharge treatment is to use a comb-shaped low-temperature plasma brush to discharge the surface where the base membrane and the dense separation layer membrane liquid are combined, and brush back and forth 2 to 3 times.

9. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (5), the dense separation layer membrane liquid is coated by blade coating or casting, and the coating amount of the dense separation layer is 20-50g / m 2 .

10. The method for preparing a hydrophobic double-layer polymer asymmetric composite membrane according to claim 1, characterized in that: In step (5), the drying is carried out in two stages, firstly at 60°C for 2 to 4 hours, and then at no more than 120°C for another 4 to 12 hours.

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